Method of cleaning and recycling glycol-tainted water from de-icing operations at airports

ABSTRACT

The invention disclosed and claimed herein relates to treatment of water contaminated with glycol to be recycled for further effective use of the cleaned water resulting therefrom, especially at airports. More specifically, this invention relates to improved techniques for efficiently and reliably generating continuous flows of cleaned water as well as a continuous flow of recyclable glycol water of controlled concentration.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of U.S. ProvisionalApplication Ser. No. 60/961,725, filed Jul. 24, 2007, which is herebyincorporated in its entirety by reference.

TECHNICAL FIELD OF THE INVENTION

The invention disclosed and claimed herein relates to treatment of watercontaminated with glycol to be recycled for further effective use of thecleaned water resulting therefrom, especially at airports. Morespecifically, this invention relates to improved techniques forefficiently and reliably generating continuous flows of cleaned water aswell as a continuous flow of recyclable glycol-water concentrate ofcontrolled concentration.

BACKGROUND OF THE INVENTION

The formation of ice on the wings of an airplane can reduce the lift andincrease the drag by degrading the performance of the airfoil.Additionally, the ice may break away from the wing and be ingested by anengine, possibly causing a failure of the engine and endangering thesafety of the passengers of the aircraft. To remove and prevent thebuild-up of ice on the wings, the skin of the wings can be sprayed witha fluid that has a low freezing point, such as a glycol. In coldclimates the wings are typically sprayed at the airport before takeoff.The glycol forms a protective layer on the aircraft. The glycol has lowshear strength and allows the ice to be sheared from the wings. Wingsare sprayed with a heated dilute glycol solution (propylene, ethylene ora mixture of the two, in water). The solution typically also holdswetting agents, rust inhibitors, flame retardants, thickeners and othermaterials, depending on the Class of the solution being used, anddepending on the nature of other fluids that are deposited to airportrunways and roads during daily operations.

Conventional aircraft deicing by hot deicing fluid (Type I) washdownfrom ground or mobile boom systems has been in use for decades with nobasic changes to this technology other than refinements to the deicingfluid heating and application systems. Some of the patents coveringconventional deicing and its refinements are as follows U.S. Pat. No.3,243,123, to D. M. Ingraham, et. al., issued Mar. 29, 1966; U.S. Pat.No. 4,073,437 to Thornton-Trump, issued Feb. 14, 1978; U.S. Pat. No.4,826,107 to Thornton-Trump, issued May 2, 1989 and U.S. Pat. No.5,028,017, to Simmons, et al., issued Jul. 2, 1991. Other publicationsdescribe various deicing systems to improve the deicing process, eitherby reducing or eliminating the use of glycol, or by applying glycol in amore efficient manner such that the glycol usage is reduced forinstance: U.S. Pat. No. 5,244,168 to Williams, issued Sep. 14, 1993 forA Methodology And Apparatus For Forced Air Aircraft Deicing and U.S.Pat. No. 5,104,068 to Krilla et al., issued Apr. 14, 1992.

Presently, aircraft deicing is carried out by applying glycol baseddeicing fluids, which may be propylene glycol, ethylene glycol or amixture of the two glycols.

These fluids are sprayed on aircraft to lift accumulated ice and it isbelieved that propylene glycol prevents ice buildup. Numerouscomposition and method patents exist on this application and have beendisclosed in U.S. Pat. No. 4,191,348 to Holwerda; U.S. Pat. No.4,254,821 to Matsuda et al.; U.S. Pat. No. 4,573,802 to Kerrigan et al.;U.S. Pat. No. 4,826,107 to Thornton-Trump; U.S. Pat. No. 5,096,145 toPhillips et al.; U.S. Pat. No. 5,244,168 to Williams; and U.S. Pat. No.5,845,848 to Amako et al., and of which are incorporated herein byreference.

Most of the glycol that is sprayed onto the wings falls off of the planeand flows into a drainage system which removes the de-icing fluid. Anaircraft is typically sprayed with gallons of dilute and heated de-icingfluid that is used only one time.

Another drawback of certain prior art deicing fluids is the highchemical and biological oxygen demand that make them environmentallyunfavorable. The glycols are exemplary of deicing fluids thatparticularly suffer from this type of environmental drawback, and mostmunicipalities govern the amount of glycol-tainted water that can bereleased to local water treatment facilities.

It would be desirable to provide a recovery system that can collect andrecycle both the water from glycol-containing water as well as theglycols from de-icing fluid sprayed onto an airplane so that both thewater and the fluid can be reused.

Recycling the de-icing fluid would decrease the cost of spraying theaircraft by providing a recyclable product that may be used for avariety of alternative uses. Recycling the water from de-icingoperations would also reduce overall costs by eliminating the cost tomunicipalities and the airports which must control the release ofglycol-tainted water, as well as providing a beneficial use of the waterat the airport location, saving the cost of using fresh water or waterfrom the associated water authority. Another benefit of recycling thewater recovered from RDAF is that the recovered water will not containundesirable materials typically found in a municipal water supply (suchas minerals, etc.).

Most attempts to adapt MVR for use in recycling glycol from de-icingoperations have been less than completely successful as many suchoperations release treated water into the local sewer system ortransport the treated water off-site.

Some prior art systems may use reverse osmosis in order topre-concentrate the dilute glycol de-icing fluid prior to use of MVR.

Most other systems do not provide a resultant glycol concentrate athigher concentrations which may require further concentration of thefluid or, if the more dilute concentrate is shipped, will requiregreater shipping volume.

It would also be desirable to have such recycling occur in a continuousprocessing (or continuous batch processing) and to be able to producetwo recycled products in the same operation at an airport site, withoutthe environmental risk of releasing glycol-containing water to the localwater shed or water treatment facility.

It is also desirable to be able to produce a glycol concentrate that canbe efficiently shipped for reformulation into a variety of recycledproducts for other industrial uses.

SUMMARY OF THE INVENTION

The present invention relates to a method and apparatus for separatingwater from glycol-containing water, such as that collected at airportsfrom deicing operations.

Mechanical Vapor Recompression (MVR) Evaporation is an energy efficientprocess that produces high quality distilled water from wastewatercontaining dissolved glycol. With evaporation, high quality water isboiled from wastewater and can be later condensed as distilled water.The glycol(s) remain in solution and are removed from the system asconcentrated blowdown. Concentrate may removed from the system at acontrolled rate so that the glycol concentration in the apparatusremains at the desired value. Concentrate does not pass through asecondary heat exchanger to recover energy.

Producing distilled water from direct-fired distillate requiresapproximately 970 BTU/lb of heat energy, at a liquid temperature of 212°F. and at atmospheric pressure. Due to the sophisticated heat exchangerconfiguration in MVR evaporation, distilled water can be theoreticallyproduced with only 25-28 BTU/lb, 1/40th the energy.

Examples of mechanical vapor recompression systems, such as multi-effectevaporation system from which the present invention may be constructedand practiced, are described in U.S. Pat. No. 4,270,974 and U.S. Pat.No. 5,076,895, the disclosures of which are hereby incorporated byreference. Other patents describing MVR include U.S. Pat. Nos.6,375,803; 6,638,398; 6,733,636; 7,077,201 and 7,150,320, thedisclosures of which are hereby incorporated by reference.

Other such systems, such as the preferred system, may be obtainedcommercially from Clean Water Ltd. of Columbus, Ohio.

It has been discovered that MVR may be used in a continuous system toproduce both water clean enough for such uses as non-potable uses at theairport itself, while also providing a continuous flow of a high value,reusable glycol concentrate.

Accordingly, the present invention includes a method of removing andrecycling water from glycol-containing water collected at an airportfollowing use of the glycol as a de-icing agent, the method comprising:(a) collecting water containing the glycol in a holding vessel at anairport; and (b) removing water from the collected water containing theglycol by an evaporative process; and (c) recycling the water for use atthe airport.

The water may be collected from de-icing operations in accordance withknown methods and apparatus, typically directed to holding tanks fromwhich the glycol-containing water may be transported in trucks orconducted through conduits directly to the MVR system.

The water is removed from the glycol-contaminated water through anyevaporative method, such as that described herein. The water produced byuse of the method and apparatus of the present invention is ofsufficiently high purity that it may be used direct in a wide variety ofnon-potable uses on the airport grounds.

With respect to the recycling of the cleaned water, it may be used forany purpose appropriate for the quality of the resultant water. Forinstance, the water may be recycled for a use such as one or more usesselected from the group consisting of (1) grounds irrigation, (2)cleaning of aircraft, (3) runway cleaning at the airport and/or (4) as acoolant in HVAC systems.

The invention also includes a method of continuously removing water fromglycol-containing water collected at an airport following use of theglycol as a de-icing agent, the method comprising: (a) collecting watercontaining the glycol (RADF) in a holding vessel at an airport orconducting the water containing the glycol in a conduit directly fromthe de-icing site, the concentration of the glycol in water containingthe glycol being less than 35%, and more typically well less than 5%;and (b) continuously removing water from the collected water containingthe glycol through a monitored mechanical vapor recompression system, soas to produce a flow of water containing the glycol having aconcentration in the range of from about 35% to about 45%.

In a preferred method variation, this may be done without the use ofreverse osmosis, such that the original glycol concentration in the RADFis less than 1% (typically about 0.25%).

One of the advantages of the preferred system and method of the presentinvention is that de-icing water at relatively low concentrations (i.e.,below 5%) may be sent directly to the MVR system of the presentinvention. This is in contrast to existing systems which typically usereverse osmosis to pre-concentrate the de-icing water solution beforesubjecting it to MVR.

The present invention also includes an apparatus for removing water fromglycol-containing water, comprising: (a) a forced circulation MVR heatedevaporator and having an input conduit and an output conduit, the inputconduit adapted to direct relatively low-glycol water to the forcedcirculation MVR heated evaporator so as to evaporate water in the formof steam from the relatively low-glycol water so as to producerelatively high-glycol water, the forced circulation MVR evaporator alsoadapted to contain the relatively high-glycol water remaining afterevaporation; (b) a monitor adapted to determine the concentration ofglycol in the relatively high-glycol water remaining after or duringevaporation, and to issue a control signal in response to thedetermination; (c) a liquid output conduit, adapted to conduct a flow ofthe high-glycol water from the forced circulation MVR evaporator; and(d) a flow controller adapted to control the flow of the high-glycolwater from the forced circulation MVR evaporator in response to thecontrol signal.

It is preferred that the flow controller is adapted to control the flowof the high-glycol water from the forced circulation MVR evaporator suchthat the concentration of glycol in the high-glycol water is in therange of from about 35% to about 45%.

The resultant glycol concentrate can be efficiently shipped forreformulation into a variety of recycled products for other industrialuses, such as for coolants, dust control, windshield washer fluid, etc.

It is also preferred that the apparatus additionally comprises a steamoutlet conduit, adapted to conduct the steam from the forced circulationMVR evaporator, and a bubbler adapted to remove glycol from the steam.As an alternative, the system of the present invention may use a stackedmedia column for further removal of the glycol from the steam. Anotheroptional variation is to treat the condensed steam through reverseosmosis in order to further remove glycol from the condensed steam. Inaddition, the vapor separator may be fitted with a scrubbing column thatcan be used either; distillation trays; random packing; or stackedpacking. These devices allow the evaporator vapor holding small amountsof evaporated glycol to come into intimate contact with the dilutematerial feeding the forced circulation MVR evaporator, thereby reducingthe glycol content of the evaporated vapor leaving the column. Thedistillate produced from the evaporator, condensed evaporated vaporleaving the scrubbing column) may be processed in filtration equipment(reverse osmosis, and or ultrafiltration) to further remove glycol fromthe flow.

The method and apparatus of the present invention may be applied toairport de-icing systems that use collection tanks for capturingwater-glycol run-off from de-icing operations, such as those describedfor instance, in U.S. Pat. No. 6,820,841, which is hereby incorporatedby reference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an MVR system in accordance with one embodimentof the present invention that may be used in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with the foregoing summary, the following present adetailed description of a preferred embodiment of the present inventionwhich is currently considered to be the best mode thereof.

FIG. 1 is a schematic of an MVR system that may be used in accordancewith one embodiment of the method of the present invention. This systemmay be used to produce cleansed (distilled) water which in turn may beutilized for a wide variety of uses at the airport, such as for airplanecleaning, irrigation and other non-potable uses. The distilled water maybe conducted from the MVR system of FIG. 1 through conduits to anairplane cleaning hangar or facility, or to irrigation lines for theairport grounds.

Recovery of high quality water (distillate) from recovered aircraftdeicing fluids may be accomplished using a forced circulationevaporation system commercially available from Clean Water Ltd. ofColumbus, Ohio. The recovered aircraft deicing fluid primarily containspropylene glycol, ethylene glycol or a mixture of propylene and ethyleneglycols, in water. The aircraft deicing fluid also contains very minoramounts of wetting agents, rust inhibitors, flame retardants,thickeners, machine oils, and other materials that are deposited ontoairport roads and run-ways during daily operations. These minorcomponents may be removed or treated following collection of the RADFconcentrate.

FIG. 1 is a schematic of an MVR system in accordance with a preferredembodiment of the present invention, and that may be used in accordancewith the method of the present invention. FIG. 1 shows a MVR systemmodified to better perform the preferred methods of the presentinvention.

FIG. 1 shows the main components of the preferred evaporation system,that are as follows:

-   -   (a) Recovered Dilute Aircraft Deicing Fluid storage tank.    -   (b) Evaporator Feed pump (centrifugal type).    -   (c) Feed bag filter station.    -   (d) Distillate preheating using direct steam injection.    -   (e) Feed Preheating against distillate heat exchanger (shell and        tube or plate type).    -   (f) Flash Vessel (vapor body).    -   (g) Concentrate Circulation Pump.    -   (h) Evaporated Vapor Scrubbing Column.    -   (i) Mechanical Vapor Recompressor (e.g., Centrifugal or Positive        Displacement Type)    -   (j) Circulated Fluid Heater (shell and tube of plate type).    -   (k) Concentrated Recovered Aircraft Deicing Fluid Extraction        Pump (Centrifugal or Positive Displacement Type)    -   (l) Distillate Bottle    -   (m) Distillate Pump

The product path through the system may proceed as follows:

Dilute Recovered Aircraft Deicing Fluid (RADF) is typically collected atthe airport of interest and normally is transferred by truck or othermeans (such as dedicated pipes or gutters or other fluid conduits) tothe Recovered Aircraft Deicing Fluid storage tank (a) (the fluid mayalso be collected and delivered directly to the system without the useof a storage tank although the liquid volumes involved typically willrequire large storage tanks). Evaporator Feed Pump (b) routes the RADFfrom storage tank (a) through the Bag Filter Station (c) to removesuspended matter, and then further through the Feed Preheater (e)delivering the controlled flow to the top of the Evaporated VaporScrubbing Column (h) (which optionally may include a bubbler or a traycolumn, randomly packed column, or a stacked media column ). The DiluteRADF passes down through the Evaporated Vapor Scrubbing Column,contacting evaporated vapor, falling into the concentrated RADF in thelower part of the Flash Vessel (f).

Concentrate Circulation Pump (g) continuously delivers the RADF to theCirculated Fluid Heater (j) which raises the temperature of the flow.The heated Circulated Flow is delivered back to the Flash Vessel (f)where flash evaporation takes place as the pressure in the flash vesselis lower than the saturated temperature of the Circulated Fluid leavingthe Circulated Fluid Heater.

Evaporated vapors (generated in the flash evaporation process)containing propylene glycol, ethylene glycol or a mixture of propyleneand ethylene glycol (glycol) flow up through the Evaporated vaporScrubbing Column, coming into contact with the Dilute RADF feeding theForced Circulation Evaporation System. The Evaporated vapors leaving thetop of the column, now containing a reduced glycol concentration arerecompressed by the Mechanical Vapor Recompressor (i), and are deliveredto the Circulated Fluid Heater, where the majority of the vaporscondense, forming the Distillate (high quality recovered water, whichmay the be conducted or transported elsewhere on the airport grounds forfurther use). The Distillate accumulates in Distillate Bottle (l),fitted with a level control system. The level control system modulatesthe operation of Distillate Pump (m) as necessary, removing theRecovered High Quality Water from the Clean Water Ltd. ForcedCirculation Evaporation System.

Extraction Pump (k) maintains the level in the lower part of the FlashVessel, routing the concentrate to the Concentrated RADF receiveroutside of the evaporation system.

The Flash Vessel is pressure controlled. The concentrated RADF fluidboils at a pressure and corresponding saturated liquid and vaportemperature at or above atmospheric pressure. Steam addition typicallyis used to maintain the pressure in the Flash Vessel.

The MVR system shown in FIG. 1 also preferably includes a monitoradapted to determine the concentration of glycol in the relativelyhigh-glycol water in the forced circulation MVR evaporator, and to issuea control signal in response to the determination.

The system also includes a liquid output conduit adapted to conduct aflow of the high-glycol water from the forced circulation MVRevaporator; and a flow controller adapted to control the flow of thehigh-glycol water from the forced circulation MVR evaporator in responseto the control signal, to produce a flow within a desired orpre-determined concentration range. This may be done by assay of anappropriate property of the high-glycol water in the forced circulationMVR evaporator, such as viscosity, pH, electrical conductivity, boilingpoint elevation, etc. Sensors or monitors for assaying any of theseproperties may be selected from those known and used in the art, and thecontrol circuitry may be of any type known and used in the art for thispurpose.

For instance, the Concentrated Recovered Aircraft Deicing FluidExtraction Pump (k) may be governed by a control unit adapted to providefeedback control to the Concentrated Recovered Aircraft Deicing FluidExtraction Pump so as to maintain a relatively steady flow ofhigh-glycol water at a known concentration (or concentration range) fromthe system, typically and preferably 35% to 45%, most preferably about40%. This will allow the operator to control the output concentrate ofthe system while providing that the energy through the evaporator is notso great that the quality of the water distillate is compromised byglycol content.

In addition, the system of the present invention may also be monitoredand controlled so as to produce condensed water from the evaporator ofdesired or pre-determined high quality.

The scrubbing column (h) may incorporate trays that allow intimatecontact between the evaporated vapor having a small glycolconcentration, and dilute RDAF.

In a preferred embodiment, a bubbler may be provided for further removalof glycol from the steam outgoing from the evaporator. The bubbler maybe in the form of a perforated plate above the evaporation surface(s)and having apertures through which perforations the steam may pass. Eachof the apertures is provided with a condenser plates (preferablyconcave) disposed above each aperture against which the steam strikes,causing small amounts of glycol remaining in the steam to condense ontothe underside of these condenser plates. The inlet conduit may dispensethe dilute RADF fluid above the plate so that it forms a shallow bathatop the perforated plate before pouring through the apertures or overthe edges to the evaporator surface. This flow of in-coming dilute RADFpicks up small droplets of glycol to be returned to the evaporatorplate(s) and the lower portion of the flash vessel.

The deicing fluid normally has a glycol content of 15-25 weight percent(monopropylene, monoethylene or diethylene) with an addition ofthickener, normally a maximum of 1% of the total amount of glycol. Theconcentration range may extend to lower values, the dilution dependingon the freezing point depression required, and this in turn is afunction of weather and wait time prior to aircraft takeoff

In addition, additives of anionic and/or nonionic tensides, corrosioninhibitors and, in certain cases, colorings in a mixture with water,solid particles, salts etc. are included. Since the deicing fluidnormally is buffered, it has a pH of about 6-8.

The RADF once collected may have a concentration of glycol well below 5%(typically about 0.25%). The present invention allows for the collectedRADF to be sent directly to the MVR system of the present invention,even at concentrations well below 5% and without the pre-evaporative useof reverse osmosis, although other pre-concentration processes such asreverse osmosis may be used in accordance with the present invention.

All publications and patents mentioned herein are hereby incorporated byreference to the same extent as if each individual publication or patentwas specifically and individually indicated to be incorporated byreference.

Although only several exemplary embodiments of this invention have beendescribed in detail, it will be readily apparent to those skilled in theart that the novel produced waste treatment process, and the apparatusfor implementing the process, may be modified from the exact embodimentsprovided herein, without materially departing from the novel teachingsand advantages provided by this invention, and may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Therefore, the disclosures presented herein areto be considered in all respects as illustrative and not restrictive. Itwill thus be seen that the objects set forth above, including those madeapparent from the preceding description, are efficiently attained. Manyother embodiments are also feasible to attain advantageous resultsutilizing the principles disclosed herein. Therefore, it will beunderstood that the foregoing description of representative embodimentsof the invention have been presented only for purposes of illustrationand for providing an understanding of the invention, and it is notintended to be exhaustive or restrictive, or to limit the invention onlyto the precise forms disclosed.

All of the features disclosed in this specification (including anyaccompanying claims, and the drawing) may be combined in anycombination, except combinations where at least some of the features aremutually exclusive. Alternative features serving the same or similarpurpose may replace each feature disclosed in this specification(including any accompanying claims, and the drawing), unless expresslystated otherwise. Thus, each feature disclosed is only one example of ageneric series of equivalent or similar features. Further, while certainprocess steps are described for the purpose of enabling the reader tomake and use certain water treatment processes shown, such suggestionsshall not serve in any way to limit the claims to the exact variationdisclosed, and it is to be understood that other variations, includingvarious treatment additives or alkalinity removal techniques, may beutilized in the practice of my method.

Many variations of the present invention within the scope of theappended claims will be apparent to those skilled in the art once theprinciples described herein are understood. The intention is to coverall modifications, equivalents, and alternatives falling within thescope and spirit of the invention, as expressed herein above and in anyappended claims. The scope of the invention, as described herein and asindicated by any appended claims, is thus intended to include variationsfrom the embodiments provided which are nevertheless described by thebroad meaning and range properly afforded to the language of the claims,as explained by and in light of the terms included herein, or the legalequivalents thereof.

1. A method of removing and recycling water from glycol-containing watercollected at an airport following use of said glycol as a de-icingagent, said method comprising: (a) collecting water containing saidglycol in a holding vessel at an airport or conducting the watercontaining the glycol in a conduit directly from the de-icing site; and(b) removing water from said water containing said glycol by anevaporative process; wherein, after removing the water, the glycolconcentration of said water containing said glycol is in the range offrom about 35% to about 45%; and (c) recycling said water for use atsaid airport.
 2. The method according to claim 1 wherein said water isrecycled for a use selected from the group consisting of (1) irrigation,(2) cleaning of aircraft, (3) runway cleaning at said airport.
 3. Themethod according to claim 1 wherein the glycol concentration is about40%.
 4. The method according to claim 1 wherein the evaporative processcomprises: continuously removing water from said water containing saidglycol through a monitored mechanical vapor recompression system, so asto produce a flow of water containing said glycol having a concentrationof about 40%.
 5. The method according to claim 1 wherein the watercollected in step (a) has an initial concentration of glycol less than5%.
 6. The method according to claim 5 wherein the water collected instep (a) has an initial concentration of glycol less than 0.25%.
 7. Themethod according to claim 1 wherein the method is conducted at or aboveatmospheric pressure.
 8. The method of claim 1 wherein the methodfurther comprises a pretreatment step comprising a filter to removesuspended matter.
 9. The method according to claim 1 wherein the glycolis recycled for a use selected from the group consisting of a coolant,dust control, and windshield fluid.